This invention relates primarily to electronic sound masking systems in a workplace environment, but may additionally involve any combination of signals including masking, aural enhancement, paging, public address, and background music. More specifically, it relates to sound masking systems adapted for use with a suspended ceiling.
Noise in a workplace is not a new problem, but it is one that is receiving increasing attention as open workplace configurations and business models continue to evolve. A number of recent studies indicate that noise, in the form of conversational distraction, is the single largest negative factor impacting worker productivity.
As the service sector of the economy grows, more and more workers find themselves in offices rather than manufacturing facilities. The need for flexible, reconfigurable space has resulted in open plan workspaces, i.e., large rooms with reduced height, moveable partitions over which sound can pass. The density of workstations is also increasing, with more workers occupying a given physical space. More workers are using speakerphones, conferencing technologies, and multimedia computers with large, sound reflecting screens and even voice input. All these factors tend to increase the noise level in workplaces making the noise problem more difficult and costly for businesses to ignore.
In closed spaces, particularly in office and meeting room settings, speech intelligibility and acoustic performance are determined by a variety of factors, including room shape, furnishings, number of occupants, and especially floor, wall, and ceiling treatments. This acoustic environment will determine how much sound intrusion will occur as well as the level to which the listeners within these spaces will be affected by extraneous noise and conversational distraction.
A more general examination of the interior environment of a room reveals other aspects that play a major role in how sound is perceived by the occupants. Recent research has indicated that when looking at the issue of sound intrusion between spaces, the transmission loss of materials and sound absorption characteristics of materials are not the only contributors to the perceived acoustical environment. Another factor is the background noise in a space. This includes the sounds produced by overhead utilities such as heating, ventilation, and air conditioning (HVAC) ductwork. Another significant factor is the sound, much of which is conversational, that intrudes from adjacent spaces. This has become the focus of much current research. Sound can enter a space in a variety of ways. In an office setting, sound travels through walls or partitions; through open air spaces such as doorways and hallways; and through other air spaces such as HVAC ductwork, registers and diffusers. Sound intrusions may take a number of paths including 1) travel by deflection over partitions that end below the ceiling; 2) through ceiling panels, across the utility/plenum space, and back down through the ceiling; 3) through the structural ceiling deck, the utility/plenum space, and the suspended ceiling, from above; and 4) conversely through the ceiling, utility/plenum space, and ceiling deck/floor from below.
There are two approaches to mitigating the presence of undesired sounds in a space. Sound can be attenuated as it travels from the source, or it can be covered up with some sort of masking technique. It is the latter of these approaches that is the focus of this invention.
Conversational distraction and uncontrolled noise are the primary causes of productivity loss within office workspaces. The principle of sound masking involves the introduction of sound in a specified frequency range. The addition of sound at an appropriate level in the frequency spectrum occupied by the human voice provides a masking effect, in essence, drowning out the undesired sounds in such a way that it is not noticeable to the listener. A typical sound masking system includes the following elements:
1. a xe2x80x9cpink noisexe2x80x9d signal;
2. a means of filtering the signal to provide the desired spectrum of sound;
3. a means of amplification; and
4. a means of creating a uniform sound field in the area being treated.
A pink noise signal contains equal amounts of sound energy in each one-third octave band, and covers a broad frequency range which includes the speech spectrum.
Sound masking is usually accomplished by the introduction of a precisely contoured broadband sound that is constant in level over time, and sufficiently loud to mask conversational distraction and unwanted noise, but not so loud as to be annoying in and of itself. This sound is similar to that which we attribute to the HVAC system air diffuser. The system generally consists of electronic devices which generate a sound signal, shape or equalize a signal and amplify a signal. This signal is then distributed to an array of speakers that are normally positioned above the ceiling in the plenum on 12-16 foot centers. Sound masking systems in open plan offices are typically set at a sound level which corresponds to 48 dBA (dB xe2x80x9cAxe2x80x9d weighted) +/xe2x88x922 dB. This sound level generally insures conversational privacy without causing a distraction itself.
Typical electrodynamic cone loudspeakers have an acoustic radiation pattern that is very dependent upon the frequency of excitation. At low frequencies, these loudspeakers radiate sound fairly uniformly over a broad range of angles. As the frequency of the input wave increases, the sound radiation pattern produced by the loudspeaker becomes more focused and directed on-axis (like a flashlight as opposed to a floodlight). A common 6.5-inch speaker, for example, may have a forward radiation pattern approaching an omni-directional 180 degrees at 250 Hz, but when driven at 4 kHz, the majority of the forward sound energy produced is concentrated in a highly directional beam that is about 15 degrees wide.
Since conventional dynamic loudspeakers produce a directed, coherent sound field at the frequencies of interest in masking, their utilization to create a uniform, diffuse reverberant field presents a challenge.
One solution that has often been employed utilizes traditional dynamic loudspeakers mounted above a ceiling. An array of conventional dynamic loudspeakers is mounted above a suspended ceiling and driven by conventional electrical wiring. The loudspeakers are oriented to fire upwards into the hard floor slab above. This provides a longer reflective path for the sound to travel thus more evenly dispersing the sound in the plenum space. The reflected sound passes through the suspended ceiling system, where it may be further dispersed. The penalty for firing the speakers upwards, however, is that considerable additional power is required to drive the speakers to realize the desired sound levels to the listener. Pointing the loudspeakers directly down through the ceiling, or mounting conventional speakers on top of the ceiling panels, would create a non-uniform sound field at the audible frequencies of interest, with some areas sounding louder and other areas sounding softer. Compensating for this non-uniform sound field would require the use of many more speakers at considerably higher cost. What is needed is a better way to deliver sound to the desired space, and to do so in such a way with a system that is easily installed and simple to configure and change.
The present invention provides a system for mounting a flat panel sound radiator system in a standard ceiling grid system to generate the desired sound field into an architectural space immediately below. The flat panel radiator includes a stiff radiating panel, a transducer having a magnet attached to the radiating panel, a voice coil assembly attached to the radiating panel, and wiring connected to an excitation source.
Flat panel radiators (speakers) work on the principle that an exciter hooked up to the flat panels causes the panels to vibrate, generating sound. The sound that is generated by flat paneled radiators is not restricted to the cone of sound (beaming) that normal speakers generate. The vibration of the panel generates a complex random ripple of waveforms on the panel surface, which in an ideal model radiates sound in a circular pattern (omni-directional) from the panel. This differs from a standard cone speaker which can be considered as a piston, producing a beam of sound, which, in the field of stereo sound systems results in the phenomenon called the xe2x80x9csweet spotxe2x80x9d where the two beams interact most effectively for stereo sound. The omni-directional radiation pattern of the flat panel radiators means that the sound levels are equal across a large listening area.
Flat panel radiators have broad acoustic radiation patterns at the frequencies required for sound masking. As noted, the flat panel radiator includes a light, stiff radiating panel of arbitrary size, and a transducer. The transducer has a magnet clamped to the radiating panel, a voice coil assembly, also attached to the panel, and wiring connected to an excitation source. When electrical current is passed through the voice coil, the resulting combination of electromagnetic field forces with the magnetic field will induce a very small relative displacement, or bending, of the panel material at the mounting points. Rather than the coherent piston-like motion of a cone speaker, the motion of the flat panel is decidedly incoherent, containing many different complex modes spread over the entire surface of the radiator. This effect contributes significantly to the broad radiation pattern and lack of beaming behavior characteristic of this technology. This can best be achieved through a flat panel made of honeycomb cell-type material, which is lightweight and does not rust. This honeycomb material provides minimal loss and a smooth sound pressure response in the low, middle, and high frequency ranges.
The core material is typically xe2x80x9csandwichedxe2x80x9d between skins of high strength composite material. A bonding adhesive is used to attach the skin material to the honeycomb core. The resultant honeycomb panel offers one of the highest strength-to-weight constructions available.
In the novel mounting configuration described herein, a rectangular radiating panel of a flat panel radiator is supported by containment elements and placed inside a frame element. An additional isolation element may be attached to isolate the radiator panel vibrations from the normal contacts to the ceiling grid support structure. This mounting configuration improves the isolation between a vibrating element of the flat panel speaker and the support grid structure. A bridge support element is attached to the frame element in this configuration, and contains the wiring for the flat panel speaker thus avoiding contact with the radiating panel. An acoustic scrim is attached to the frame for aesthetic purposes.